FIG. 1 shows an example of the configuration of a known encoding device.
A band separator 1 separates an input audio signal into a plurality of frequency bands (27 bands in this case) and outputs signals from resultant encoding units A0 to A26 to corresponding normalizers 2-1 to 2-27 and to a quantization accuracy determination unit 3 in each predetermined time block (frame). When it is unnecessary to distinguish among the encoding units A0 to A26, the encoding units are simply referred to as the “encoding units A”. Similar notations are used in other cases.
The band separation by the band separator 1 can be performed by using a filter such as a QMF (Quadrature Mirror Filter) or a PQF (Polyphase Quadrature Filter) or by grouping spectral signals generated by spectral transformation such as MDCT in units of bands.
The encoding units A can be of the same length or can have different lengths, depending on a critical bandwidth.
The normalizer 2-1 detects the signal component having the largest absolute value from the signal from the encoding unit A0 from the band separator 1 and computes a normalization coefficient B0 for the encoding unit A0 using the detected value. The normalizer 2-1 outputs the computed normalization coefficient B0 to a multiplexer 5, and also normalizes the signal of the encoding unit A0 in accordance with a value corresponding to the normalization coefficient B0 and outputs the resultant normalized data C0 to a quantizer 4-1.
As in the normalizer 2-1, the normalizers 2-2 to 2-27 compute normalization coefficients B1 to B26 based on the signals from the encoding units A1 to A26 and output the normalization coefficients B1 to B26 to the multiplexer 5. Also, the normalizers 2-2 to 2-27 generate normalized data C1 to C26 and output the normalized data C1 to C26 to quantizers 4-2 to 4-27. The normalized data C are values within the range from −1.0 to 1.0.
The quantization accuracy determination unit 3 determines quantization steps for quantizing the normalized data C0 to C26 in accordance with the signals of the encoding units A0 to A26 from the band separator 1 and outputs quantization accuracy information D0 to D26, corresponding to the determined quantization steps, to the corresponding quantizers 4-1 to 4-27. The quantization accuracy determination unit 3 also outputs the quantization accuracy information D0 to D26 to the multiplexer 5.
The quantizer 4-1 quantizes the normalized data C0 from the normalizer 2-1 using the quantization step corresponding to the quantization accuracy information D0 from the quantization accuracy determination unit 3 and outputs a resultant quantization coefficient F0 to the multiplexer 5.
As in the quantizer 4-1, the quantizers 4-2 to 4-27 quantize the normalized data C1 to C26 using the quantization steps corresponding to the quantization accuracy information D1 to D26 from the quantization accuracy determination unit 3 and output resultant quantization coefficients F1 to F26 to the multiplexer 5.
The multiplexer 5 encodes the normalization coefficients B0 to B26 from the normalizers 2-1 to 2-27 into 6-bit codes and the quantization accuracy information D0 to D26 from the quantization accuracy determination unit 3 into 3-bit codes. Also, the multiplexer 5 encodes the quantization coefficients F0 to F26 from the quantizers 4-1 to 4-27, multiplexes various resultant data generated by encoding, and generates encoded data. The processing of the multiplexer 5 is performed in units of time blocks (frames).
FIG. 2 shows an example of the configuration of a decoding device for decoding the encoded data generated by the encoding device shown in FIG. 1.
A demultiplexer 21 decodes the encoded data, which is supplied from the encoding device, into the normalization coefficients B0 to B26, the quantization accuracy information D0 to D26, and the quantization coefficients F0 to F26, and outputs the separated pieces of data to corresponding signal component composers 22-1 to 22-27.
The signal component composer 22-1 dequantizes the quantization coefficient F0 from the demultiplexer 21 in accordance with the quantization step corresponding to the quantization accuracy information D0, thus generating the normalized data C0. Also, the signal component composer 22-1 multiplies (denormalizes) the normalized data C0 by a value corresponding to the normalization coefficient B0, thus decoding the signal of the encoding unit A0, and outputs the decoded signal to a band combiner 23.
As in the signal component composer 22-1, the signal component composers 22-2 to 22-27 dequantize the quantization coefficients F1 to F26 from the demultiplexer 21 in accordance with the quantization steps corresponding to the quantization accuracy information D1 to D26, thus generating the normalized data C1 to C26 Also, the signal component composers 22-2 to 22-27 multiply (denormalize) the normalized data C1 to C26 by values corresponding to the normalization coefficients B1 to B26, thus decoding the signals of the encoding units A1 to A26, and output the decoded signals to the band combiner 23.
The band combiner 23 combines the bands of the signals of the encoding units A0 to A26 from the signal component composers 22-1 to 22-27, thereby decoding the original audio signal.
In known encoding devices, as described above, the normalization coefficient B corresponding to one encoding unit A is uniformly encoded into, for example, 6-bit data. In other words, the total number of bits of codes for the normalization coefficients B0 to B26 corresponding to the encoding units A0 to A26 is 162 (=6×27) bits per frame.
In known encoding devices, the quantization accuracy information D corresponding to one encoding unit A is uniformly encoded into, for example, 3-bit data. In other words, the total number of bits of codes for the quantization accuracy information D0 to D26 corresponding to the encoding units A0 to A26 is 81 (=3×27) bits per frame.
As described above, since many bits are used to encode the normalization coefficients B and the quantization accuracy information D in known encoding devices, the total number of bits of the encoded data is increased. It is thus difficult to improve the encoding efficiency of encoded data.